This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP99/03936 (published in Enqlish) filed Jul. 22, 1999.
This invention relates to an orientation angle detector using gyroscopes and, in particular, to compensation or correction of orientation angle measured by the, gyroscopes in such an orientation angle detector.
In the prior art, an orientation angle detector is used for head tracking in virtual environment, augmented reality and teleoperator systems using head mounted displays (HMDs). It can also be used as an input device for computers.
A known three dimensional (3-D) orientation angle detector comprises three gyroscopes (which will be referred to as xe2x80x9crate gyrosxe2x80x9d) disposed in three orthogonal axes on a moving body to obtain three orthogonal angular rates or velocities. The orthogonal angular rates are integrated to produce three angular factors representing the orientation angle. The, orientation angle, is usually represented by X-Y-Z Euler""s angle. xcex8=(xcex1, xcex2, xcex3). The known orientation angle detector is disclosed in a paper by Yamashita et al, entitled xe2x80x9cMeasurement of Human Head Motion using A Three-Dimensional Posture Angle Sensorxe2x80x9d, National Convention Record of I.E.E. Japan, Vol. 3 (1997), p.p. 304-305.
In order to compensate errors integrated in integration of the angular velocities measured by the rate gyros, it is also known, as is also disclosed in the paper mentioned above, to use three accelerometers which are also disposed in the same three orthogonal axes to measure acceleration in the three orthogonal directions. Another set of three angular factors representing the orientation angle is calculated from the measured acceleration, and is used for estimation and correction of the orientation angle measured by the rate gyros.
Fiber optics gyroscopes (FOGs) and semiconductor accelerometers are usually used for the rate gyros and the accelerometers. The FOG is excellent in its accuracy but is very expensive. A Coriolis vibratory gyroscope known as a piezoelectric vibratory gyroscope is economically useful because of its low cost but is low in its accuracy.
It is an object of this invention to provide an orientation angle detector which has excellent-accuracy and which is simple in structure, and which can use FOGs for the rate gryos but can also use Coriolis vibratory gryoscopes to lower the cost of the detector without significant degradation of accuracy in comparison with use of FOGs.
According to this invention, an orientation angle detector is provided which comprises a plurality of gyroscopes disposed in parallel with a plurality of orthogonal axes (Xs-Zs) defining a detector co-ordinate on the detector, respectively, for measuring angular velocities (Jx, Jy, Jz) around respective axes (Xs-Zs), a motion angle calculator coupled to the plurality of gryoscopes for calculating a motion angle (xcex94X, xcex94Y, xcex94Z) from the angular velocities (Jx, Jy, Jz), at least one accelerometer disposed in parallel with at least one of the orthogonal axes (Xs-Zs) for measuring acceleration (Ax, Ay), a static angle calculator coupled to the at least one accelerometer for calculating a static angle (R, P) from the acceleration (Ax, Ay) and an orientation angle calculator coupled to the motion angle calculator and the static angle calculator for integrating the motion angle (xcex94X, xcex94Y, xcex94Z) to an integrated angle and calculating an orientation angle (xcex1, xcex2, xcex3) from the integrated angle and the static angle (R, P), wherein the orientation angle (xcex1, xcex2, xcex3) is an angular difference between the detector co-ordinate (Xs-Ys-Zs) and a reference co-ordinate (X-Y-Z) in a space including the detector, wherein two magnetometers are disposed in parallel with two fo the plurality of orthogonal axes (Xs, Ys) to measure terrestrial magnetic components (MX, My) in the two of the plurality of axes (Xs, Ys) and wherein the static angle calculator is coupled to the two magnetometers for calculating an azimuth from the terrestrial magnetic components (Mx, My) to produce from the azimuth an azimuthal deviation angle "PHgr" from the reference co-ordinate (X-Y-Z) as an additional factor of the static angle (R, P).
Further, according to this invention, orientation angle detectors as described in dependent claims.